


Once a Sinner

by paranoiapersonified



Series: The Trash Ship Collection [2]
Category: Gravity Falls
Genre: HUGE Age Gaps, Implied Twincest, Light Bondage, Like super light, M/M, Masturbation, Sexual Fantasy, Someone needs to stop me, Sorry Not Sorry, Switch!Dipper, Switch!Stan, Twincest, Underage - Freeform, i'm total trash, incestual thoughts
Language: English
Status: Completed
Published: 2015-07-02
Updated: 2015-07-02
Packaged: 2018-04-07 07:04:44
Rating: Explicit
Warnings: Underage
Chapters: 1
Words: 2,011
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/4253952
Author URL: https://archiveofourown.org/users/paranoiapersonified/pseuds/paranoiapersonified
Summary: <blockquote class="userstuff">
              <p>Stan wakes in the middle of the night with memories of his brother and some very, <em>very</em> dangerous thoughts of his great nephew on his mind.</p><p>Please read the tags!!</p>
            </blockquote>





	Once a Sinner

**Author's Note:**

> Oh god, okay, more of the Trash Ship. This isn't the oneshot I thought I was going to write (which I still might do anyway, eh). In fact, I wrote all of this in one night in a feverish haze because _oh my god, **switch!Dipper**_. I don't ... I can't even begin to apologize for this, I don't feel sorry at all, oh man. ((Although I do feel a little worse knowing that it's basically been confirmed that Grunkle Stan is actually Grandpa Stan, whoops.))
> 
> This is sort of in the same world as Only the Worst Kind. You can choose to view it as a prequel if you'd like, but it can also just be a stand alone story. No need to read Only the Worst Kind first, although if you like this, you might want to check it out too. 
> 
> Enjoy. We're all trash.

Stan lays back on his bed. This isn't something he normally had to do—isn't something he normally wants to do—but the dream left him with a deep, unsettling ache, stirring so deep and so strong, it was impossible to ignore.

He bites his lip as he takes himself in hand, eyes flitting to the his unlocked door—there was usually never reason to lock it—and prays that tonight is like every other night, that no wandering child comes knocking on his door.

The dream is still vivid, burning behind his eyelids. He closes his eyes and allows his imagination to take him back almost 70 years. His brother had been rocking against him, clambered over him on Stanford's old bed. It isn't really a memory, but it isn't quite fictional either. It was set too early, though, they were too young. Behind Stanford's eyes was a 12 year old, awkward and uneasy about the way his hips rolled, about the way his nails dug into Stanford's bright blue sheets.

Stan groans, soft and quiet, thoughts jumping to the actual memory, only four years later, when Stanley had been far more forceful, hips snapping with a careful and precise efficiency. God, Stanford had lasted all of a mortifying two minutes before coming in his own briefs. He hadn't even had skin contact, just the perfect friction of the soft cotton, the sight of sweat dripping down Stanley's neck, the gentle tug of Stanford's teeth on his own lip.

But he doesn't linger too long on the memory, the broad shoulders and long, lean legs revert back to noodly limbs, bony, narrow joints.

Stan runs his thumb over the tip swirling some precum over his sensitivb foreskin, and he has to bite his lip hard to keep from moaning. He had been the same age as Stanley in the dream, but his memory of that age are fuzzy with the dirty lens of decades. He tries to remember what his body felt like then, how narrow his hips were, how awkward his own arms felt, but it slowly slips in and out. His small, smooth stomach—so thin you could see his hipbones like roots peeking out below the dirt—is replaced with his current one, gray and dark dusting of hair and the soft padding of flab hiding the strong muscles he's been proud to keep. He hands, tangled fast and firm in the sheets, grow strong and calloused and knobby. Stanley's delicate legs have to spread wider to fit around Stanford's thighs. In the fantasy, Stanley moans as he shakily presses harder against Stanford's now full grown erection, which Stanford generously rolls back hard against the child.

Stan's hips—his real ones—snap up to meet his downstroke, mouth now open and gulping down air like there wasn't enough. He runs his shaky fingers through his sweat-damp hair at the thought of Stanley's small cry. His thoughts run rampant, suddenly unable to focus on just one thought. He imagines flipping Stanley over, rutting mercilessly into the boy until _he's_ the one cumming into his underwear with Stanford's name on his lips. He imagines his tongue dragging over every inch of the smooth, unmarred skin, tracing trough and tasting the sweat on his neck, his chest. He imagines taking him in his mouth, still small and thin, so that he wouldn't even have to use his throat to fit all of him in his mouth.

The taste of Stanley is something he'll never forget—has never forgotten in 60 odd years—salty and bitter and still somehow sweet and perfectly _Stanley_ through and through. He accidentally lets a groan slip through his teeth at the thought of dragging an orgasm out of Stanley, not letting up until the last of the tremors were finished with him and Stanley would have to plead for Stanford to stop dragging his tongue over his oversensitized tip, tonguing at the slit to get at more of that wonderful taste.

 _"Fuck!"_ Stan whines, hips jutting in time now with his hand, pace quickening. Oh god, the things he could do now, the things he's learned over the years, that he was too shy, too uncertain, to try when they were young. He wishes he had _known_ , known it wasn't just him, known he wasn't some monster for the thoughts in his head, for the things he wanted to do with Stanley—do _to_ Stanley. He had hated himself for years, so afraid and so _lonely_ , not being able to go to his brother for help.

His mind wanders close to the first time Stanford had touched Stanley, edging quietly and quickly, as if treading on dangerous ground—like imagining sucking off his 12 year old twin wasn't dangerous enough—when suddenly it flips. An accident, truly. Some innocuous, fleeting thought interrupts quietly, reminding him that he needed to buy some more of that cereal Dipper likes. Something small. Purely innocent, utterly unrelated to hand on his cock and the harshness of his breath. But his train of thought is derailed. Derailed horrifically. It skids of the tracks, screeching terribly as it barrels uncontrollably into _truly_ dangerous—utterly perilous—territory.

Like how similar Dipper is to Stanley when he was that age. How identically their habits—idly chewing on pens, chasing blindly after the supernatural—matched up. How even their bodies looked the same, scrawny arms and thin chest with the _perfect_ shade of lush pink dusting their shoulders when they got embarrassed or bothered ... or _aroused_.

Oh no. No. No. _No._

Stan's hand freezes, body deathly still, as he tries desperately to block the thought. But this derailed train has no breaks, and his mind is mashing the two together, imagination supplying whatever his own memory lacks. What Stanley looks like flushed with arousal quickly becomes Dipper's face, burning bright red with heat, bright brown eyes lidded and unfocused, mouth open just slightly, just enough to see the wet pink of his tongue peeking out. His chest heaves with the soft pants and gasps, and Stan can't stop the ungodly heat that spreads like wildfire through him—from his neck, down his arms, to his toes, blazing through his chest and coiling tight and white hot just below his stomach. Within seconds he is on fire with fierce _need_ and icy, chilling _fear_ blended together in some terrifying, potent thrill. He can feel his heart hammering in his chest, and it feels like all of the air drained from the room, his labored breathing can't seem to get any actual oxygen.

Carefully, apprehensively, he moves his hand down his cock in a slow motion. Then back up, all the way past the tip (the image changes subtly—Dipper's head tossed back, whine breaking high in his throat). Back down again. Up again (this time Dip's hands touch gently, cautiously, over his chest, fingertips just barely grazing his skin, over his collarbone, down his pec, dusting shyly over his nipples). And back down (they roam lower, down over his stomach, where he lets out an embarrassed, squeaky huff, tickled by his own touch, until they rest, almost teasing—but too innocently, too naively—just above his pelvis). Stan bites his lip, eyes screwed shut tightly, as he begins again, the swirling, thrilling mass of nerves inside him unsure whether to be pleased or horrified.

But his imagination takes no time in assaulting him with fresh fuel for the fire, thoughts of Dipper apprehensively taking his own member in hand, chewing on his lip as his delicately pleased himself, of Dipper straddled wide across Stan's thighs, of his lips soft against his own, his deceptively soft curls and how they would feel under his hands, through his fingers.

His mind settles on the thought of what Dipper's small erection would feel like in Stanford's palm, slicked slightly with sweat and a little bit of spit. He doesn't know for certain—thank _god_ —what Dipper looks like naked. At first he picture's Stanley's erection, somewhat thin, curled almost imperceptibly to the left, foreskin thick around the head, but it changed little by little. Slightly thicker, circumsized with a heavy red head that was still sensitive, and pebbly veins that danced along the underside. Dipper would have to bite his lip when Stan traced his thumb along those veins, pressing in with just enough pressure to make the nerves sing. He'd gasp, mouth open in a silent cry when Stan sets a relentless pace, twisting his wrist with every stroke. He'd have to cover his mouth, want to hide his face from Stan, as he'd cry out, high and long.

Subconsciously, his own hand begins to match his fantasy stroke for stroke. He is so close, so,  _so_  close, the ragged heat is boiling right beneath his skin. He has to cover his mouth with his free hand to keep from moaning too loud, muffling it with his palm first, then his fingers, stroking down his tongue, dancing at the back of his throat.  _God_ , he is almost there ...

A half-thought comes to him abruptly that almost trips him up, hand faltering on a downward motion. What if Dipper were like his grandpa? What if he got off on being in control, too?

A long groan—too loud,  _shit_ —makes its way past Stan's lips, his fingers, at the thought. Oh god, what if Dipper were a switch? His mind is flooded with frantic memories of Stanley, of the rope—oh god, the ropes—of being held down by strong hands, touched lightly, of being  _teased_ and near-tortured with desire. The thoughts converge, forming a new scene, with Stan on the ground, Dipper standing in front of him. Stan's arms are bound now behind his back, tied with a length of rope that wraps up and down his forearms, securing him in place. Dipper smiles behind his fingers, idly chewing on his nails, and Stan drags his tongue up the length of him, a flush across his cheeks and pupils blown wide, eyes bright with want, but otherwise collected. He takes a step back, just out of reach now from where Stan was sitting on the ground, and takes himself in hand, stroking languidly.

Stan bites his knuckle hard enough that he tastes blood. He is almost there, he just needs ... just needs ... just a bit more ...

Dipper moans, and Stan glances up to see his eyes closed and eyebrows furrowed, hand inches from his mouth with the smallest thread of drool trailing from his pink lips to his knuckle. Stan groans, and Dipper moans again, eyes opening to look down at him. He smiles, wide and toothy, almost menacing, and brings his foot up to Stan shoulder, pressing just hard enough to tilt Stan back, keeps going up Stan feels himself threaten to topple back. His hand is still moving on his cock, and he opens his mouth in a soft moan. He leans in close, using his foothold on Stan's shoulder so that Stan has to brace himself carefully, hand slowing as he guides himself toward Stan's mouth.

Stan has to cover his mouth, completely unable to stop the moan that tears past his lips as he comes all over his hand and stomach, back arcing up off the bed and toes curling into the the sheets, but his hand doesn't stop stroking him, riding out the waves of pleasure that bleed down his spine. Finally, finally, his body drains, flopping back down against the bed. His breath is feels raw against his throat, ragged and uneven, every gasp and pant biting. He drops his hand, and idly hopes that he managed to stay quiet enough that the twins heard none of that. He feels a small trickle of ice cold fear that he wasn't, that they possibly heard him come, but his body is so otherwise relaxed—eyes beginning to droop heavily again, not one muscle in his body tense—that he manages not to care for right now.

Stan slowly drifts back to sleep.

**Author's Note:**

> If there are any typos or if you find the tone a bit weird, I'm sorry, it's 4am and I need to be awake in two and a half hours. I'll most likely go back and edit as I see fit. Thank you for reading. 
> 
> Just for your information, Stanley is totally a switch in Only the Worst Kind. Just saying. 
> 
> Feel free to suggest Trash Ship stuff if you want to see more, I'm totally open to ideas. Doesn't even have to be nsfw, I like them being cute, too.


End file.
